The present invention relates to the milling of solids by use of vortex mills, generally, and more specifically, to the controlled milling of solids thereby.
It is known in the art to provide a means for the comminution of particulate solids. Many different milling devices are known. These include, for example, grinding mills, ball mills, rod mills, impact mills, jet mills and vortex mills. With the exception of the jet and vortex mill, in order to obtain particle comminution, most mills rely on an interaction between the particulate solid and another surface, such as the balls in a ball mill, or a baffle or impact surface in an impact mill. Jet and vortex mills do not rely, for their effectiveness, on interaction with other surfaces for particle disintegration. In addition, mills generally provide a milled product having a broad range of particle sizes, including significant proportions of oversized and undersized particles. Specifically, most mills are relatively difficult to control in so far as accurately predetermining a desired final particle size or, more particularly, a specific range of particle sizes. Furthermore, avoidance of excessive proportions of either oversize or under-size particles is often problematic.
In the art a distinction is made between jet pulverizing systems or jet mills and whirl or vortex chamber mills. Generally, in jet mills, particulate solids to be milled are introduced into a chamber where the working fluid is accelerated to high speed using venturi nozzles. Moving at a high speed, particles collide with a target such as a deflecting surface or with other moving particles in the chamber. Specifically, in jet mills particles are milled as a consequence of a collision effect. Operating speeds of particles in jet mills are generally not less than 150-300 m/s. Such jet mills are described for example in U.S. Pat. No. 5,133,504. In other jet mills, introduced coarse particles collide with intersecting high speed fluid jets, to achieve a higher collision speed, as described for example in U.S. Pat. No. 4,546,926. However, in all such jet mills, the problem of producing a range of particle sizes and of controlling the extent of comminution is not fully solved, in so far as the elimination or reduction of production of undesirable, excessive, undersized particles is concerned. Furthermore, such production of undersized particles represents an increase in energy consumption.
Use has been made of whirl or vortex chambers in conjunction with jet mills for the classification or sorting of the ground material emerging from jet milling. In such combined systems the relatively coarse particles are recirculated from the whirling classifier back into the jet mill. Such systems are described, for example, in U.S. Pat. No. 4,219,164, U.S. Pat. No. 4,189,102 and U.S. Pat. No. 4,664,319. In such systems, however, vortex chambers do not effect the milling operation, but rather particle size classification.
Another development of this technology is referred to, for example, in U.S. Pat. No. 4,502,641, which constitutes a combination of jet milling with a vortex chamber. Material to be milled is introduced through a venturi nozzle into a vortex chamber at a speed of about 300 m/s. There is created, in the vortex chamber, a fluid vortex rotating at a substantially lower speed. In the course of the milling process, particles injected into the chamber rotate in the relatively slow fluid vortex and become targets for further high speed particles injected through the venturi nozzle. Collision between particles moving in the vortex and particles introduced through the venturi nozzle, results in impact comminution as in the case of jet-mills mentioned heretofore.
There are further known in the art, vortex chambers which perform so-called resonance whirl or vortex milling. This milling process differs significantly from jet milling. For example, the particle speed in whirl chambers is considerably lower than that in jet mills and the high-speed injection of feed particles into jet mills is unnecessary in vortex mills. Fluid speed through the nozzles of a vortex chamber is generally in the range 50-130 m/s, and particle rotational speed in the vortex chamber no more than 50 m/s. At such low speeds, jet mills become ineffective. Referring to WO 94/08719, WO 98/52694 and SU 1,457,995, there are described whirl or vortex chamber milling devices, fitted with tangential fluid injection nozzles, which carry out xe2x80x9cresonance vortex grindingxe2x80x9d. The working chamber includes a generally cylindrical body with one or more openings for the introduction of particulate solids. During the milling process, particles reaching the required particle size range are continuously discharged via an axial discharge duct. Further, there may be provided sound generators in the inlet fluid nozzles for interacting with the incoming fluid flow and thereby enhancing the grinding operation as described in WO 94/08719. Additionally, the chamber may be provided with a rotatable internal side-wall adapted for rotation in the direction opposite to the direction of rotation of the vortex as described in SU 1,457,995.
U.S. Pat. No. 5,855,326 to Beliavsky, the present inventor, entitled xe2x80x9cProcess And Device For Controlled Comminution Of Materials In A Whirl Chamber,xe2x80x9d describes a process for the controlled comminution of particulate solid material. The process includes the tangential injection of a working fluid into a working chamber, and the introduction thereinto of particulate solid material. A vortex is created in the chamber and the particulate material undergoes comminution. Control of the milling and the particle size is achieved by accelerating or retarding discharge of the particles from the chamber and by the interaction of particles with mechanical elements provided in the chamber. Particles are caused to move in a random manner in all directions within the vortex and to be retained within the vortex by such mechanical elements. There is further described a cylindrical whirl chamber having an inlet into the chamber for working fluid, means for introducing particulate solid material, a discharge nozzle, and one or more mechanical elements for control of the comminution process.
It is desirable to improve and increase the amount of control in respect of the milling process, particularly with regard to the extent of comminution, to the rate of comminution, to energy conservation and to predetermined particle size.
In the description of the present invention, terms such as xe2x80x9ctopxe2x80x9d, xe2x80x9cbottomxe2x80x9d, xe2x80x9cupperxe2x80x9d, xe2x80x9clowerxe2x80x9d, xe2x80x9cheightxe2x80x9d and xe2x80x9csidexe2x80x9d are utilized for convenience of description and are not necessarily intended to indicate an orientation in space.
The present invention aims to provide an improved controlled comminution of solids relative to known art.
There is thus provided in accordance with a preferred embodiment of the present invention an improved vortex mill for milling a substantially particulate solid material. The mill includes one or more working chambers having a side-wall defining a generally cylindrical, inward facing surface and a first and a second end wall arranged transversely to the side-wall. The end surfaces are formed contiguously with and transversely to the inward-facing surface, thereby to define therewith each of one or more working chambers.
The mill also includes one or more working fluid inlets for introducing a generally tangential flow of working fluid into the one or more working chamber thereby to create a vortex flow therein. One or more discharge ports are formed in one or more of the end walls, for permitting discharge of working fluid and milled material from the one or more working chambers. One or more working fluid inlets together with one or more discharge ports facilitate the vortex flow within the one or more working chambers For introducing a substantially particulate solid material into the one or more working chambers so as to be taken up in a vortex flow of the working fluid, there are one or more feed inlets, thereby to provide milling of the solid material which is discharged from one or more discharge ports.
In addition, there is apparatus for inducing controlled perturbations in the flow of the working fluid in the one or more working chambers, thereby to improve the milling of the solid material in the vortex flow.
There is also provided, in accordance with another preferred embodiment of the present invention, an improved vortex mill including an outer casing configured to surround and enclose one or more working chambers so as to be spaced therefrom and thereby to define therewith an outer fluid flow volume. The outer casing also includes one or more outer working fluid inlets for introducing a flow of working fluid into the outer fluid flow volume, thereby to induce a fluid flow therein, operative to discharge through an inner working fluid inlet into the one or more working chambers.
Furthermore, the outer casing includes one or more outer feed inlets for introducing substantially particulate solid material into one or more working chambers via one or more inner feed inlets. In addition, there are one or more outer discharge ports for permitting discharge of milled particulate solid material from the one or more working chambers via the inner discharge port.
According to a variation of a preferred embodiment of the present invention, the side-wall of the at least one working chamber is formed of at least one functional insert generally coaxially disposed within the working chamber and having a closed shape. Each of the one or more functional inserts have a generally cylindrical side-wall formed therein.
Additionally, one or more functional inserts include at least a first and a second functional insert having substantially similar configurations and a substantially similar angular orientation with respect to each other. Alternatively, one or more functional inserts include at least a first and a second functional insert having substantially dissimilar configurations with respect to each other. The dissimilar functional inserts are disposed in a predetermined configuration sequence within the working chamber. The dissimilar functional inserts, are dissimilar with respect to: diameter, height, shape of said inward facing surface, or mechanical insert elements.
In accordance with an additional embodiment of the present invention, one or more working chambers include one ore more flow restriction elements having one or more orifice formed therein. Each orifice is formed having a predetermined size, orientation and disposition, Each flow restriction element is mounted in a fixed, coaxial disposition relative to one or more functional inserts, thereby to increase dwell time of the particulate solid material to be milled therewithin. Flow restriction elements have a configuration of: flat, planar, conical, frustum, convex, polyhedral, dished, or a surface generated by rotation of a line about the axis of said chamber in accordance with a predetermined geometric function. Furthermore a flow restriction element has one coaxial orifice formed therein.
Also, a flow restriction element may be formed integrally with one or more working chambers or is non-fixably supported within a working chamber. Alternatively, a flow restriction element is fixably mounted between a first functional insert and a second functional insert, thereby to control comminution of solid material.
Also, according to a variation of an embodiment of the present invention, a flow restriction element has vanes disposed thereon, thereby to deflect solid particles within the vortex flow generally away from the inward facing surface of the side-wall and generally towards the vortex axis. Alternatively, the vanes are disposed thereon, thereby to deflect solid particles within the vortex flow generally away from the vortex axis and towards the inward facing surface of the side-wall.
Also, in accordance with further variations of embodiments of the present invention, the flow restriction element includes having one or more rib-shaped baffle fixably attached thereto. Each rib-shaped baffle is concentric with the cylindrical side-wall and serves to reduce the velocity of solid particles adjacent to the flow restriction element thereby to prevent premature discharge of the solid particles.
Additionally, in accordance with a preferred embodiment of the present invention, the apparatus for inducing predetermined perturbations includes a side-wall configuration which includes a plurality of substantially planar side-walls. The apparatus possibly also includes one or more working fluid inlets formed within a formed recess located between adjacent substantially planar side-walls, the inlet being disposed substantially parallel to the substantially planar side-walls and generally tangentially with respect to the working chamber. Furthermore, the apparatus possibly includes one or more auxiliary working fluid inlets formed within one or more of the plurality of substantially planar side-walls. The auxiliary working fluid inlets are disposed substantially non-parallel to the substantially planar side-walls with respect to the working chamber. The one or more auxiliary working fluid inlets are provided to introduce auxiliary working fluid flow into the working chamber, thereby to cause controlled perturbations in the vortex flow and also thereby to redirect flow of particles away from the planar side-wall across the vortex flow. Another side-wall configuration includes at least one substantially planar side-wall formed within the generally cylindrical inward facing surface.
Alternatively, one or more auxiliary working fluid inlets are formed in the side-wall, and are directed substantially non-tangentially to the side-wall and at a predetermined angle to the direction of vortex flow at a point of entry of working fluid. Thereby, additional working fluid flow is introduced generally non tangentially into the working chamber, thereby to create controlled perturbations in the vortex flow and also to redirect the flow of particles away from the side-wall across the vortex flow. Another alternative relates to one or more mechanical insert elements disposed on the inward-facing surface, parallel to the axis of the working chamber. The mechanical insert element has a curved surface so as to be generally disposed away from the inward facing surface and towards the working chamber axis. In this way, the flow of working fluid and particles of solid material is redirected away from the inward facing surface, and predetermined perturbations are induced in the flow of working fluid.
A further alternative provides that one or more auxiliary working fluid inlets are disposed in the inward-facing surface. The one or more auxiliary working fluid inlets are associated with the one or more mechanical insert elements. Thereby, the flow of working fluid and particles of solid material are redirected away from the inward facing surface and induce predetermined perturbations in the flow of working fluid. One other alternative is the disposition a mechanical elastic oscillation generator on the inward facing surface, to induce predetermined perturbations in the flow of working fluid, In accordance with a further embodiment of the present invention, the apparatus for inducing predetermined perturbations in the flow of the working fluid includes apparatus for controlling the entry flow rate of working fluid, the rate of introduction of substantially particulate solid material into the working chamber, for varying the working fluid pressure in the working chamber and the rate of discharge of particulate solid material. Moreover, the apparatus for inducing controlled perturbations in the flow of the working fluid is operative to limit the frequency to within the range 5 Hz to 5.104 kHz.
In accordance with another embodiment of the present invention, each of the end walls has a shape that is either flat, planar, conical, frustum, convex, polyhedral, dished or has a surface generated by rotation of a line about the axis of the chamber in accordance with a predetermined geometric function.
Additionally, a relationship between diameter and height of the inward facing surface of the generally cylindrical side-wall, in accordance with one other embodiment of the present invention, is defined in accordance with a predetermined geometrical expression, more specifically H less than 2.5D, in which D is the diameter of the generally cylindrical side-wall inward facing surface and H is the height thereof.
In accordance with other embodiments of the present invention the one or more feed inlets are disposed in the end wall, orientated, co-axially with the working chamber, co-axially with the discharge port or eccentrically to the axis thereof. Alternatively the one or more feed inlets are disposed co-axially with the discharge port formed in the first end wall, with a distal end of the one or more feed inlets fixably attached to the inner surface of the second end wall. Then again, the one or more feed inlets are disposed in the side-wall or in the end walls.
In accordance with further embodiments of the present invention, the one or more feed inlets include a baffle apparatus generally disposed at a distal end of the feed inlet. The baffle reduces the kinetic energy of feed particles entering the working chamber through the feed inlet, and reduces feed particle velocity. Particle flow into the working chamber is thus diffused. Furthermore, the one or more feed inlets communicate with the working chamber via a transverse opening in a distal end of the feed inlet, a slot opening orientated parallel to the axis of the working chamber or orientated at a predetermined angle to the axis of the chamber. In addition, the one or more feed inlets include apparatus for introducing a flow of substantially particulate solid material into the chamber at a selected rate. This apparatus includes an ejector, the ejector drawing feed solid material from a feed vessel and, thereafter introducing a flow of substantially particulate solid material into the chamber.
In accordance with other embodiments of the present invention, the one or more discharge ports formed in one or more of the end faces is formed substantially coaxial with respect to the working chamber, and is configured to be circular or annular. Further, the configuration of the one or more discharge ports formed in one or more of the end faces is defined accordance with an expression Soutlet greater than 10xe2x88x923D2, in which Soutlet is the cross-sectional area of the discharge port; and D is the diameter of the inward facing surface. In addition, the one or more discharge port includes apparatus for separating discharged milled particulate solid material from working fluid and apparatus for collecting discharged milled particulate solid material.
In accordance with a further embodiment of the present invention, the one or more feed inlets and the one or more discharge ports are substantially mutually co-axial.
In accordance with other embodiments of the present invention, one or more auxiliary discharge ports are formed in the cylindrical side-wall or in the end walls. These auxiliary discharge ports include means for discharging partially milled particulate solid material from the one or more auxiliary discharge port and for receiving discharged partially milled particulate material from the one or more auxiliary discharge port. Partially milled particulate material is re-introduced into one or more working chambers via a conduit and an auxiliary feed inlet. This auxiliary feed inlet may be coaxially formed with the feed inlet.
According to another embodiment of the present invention, one or more recesses are formed in either the inward facing surface of the generally cylindrical side-wall or one or more of the end walls, thereby to induce a controlled perturbation in the vortex flow.
Further, one or more recesses include one or more working fluid inlets, feed inlets for particulate solid material or discharge ports for comminuted particulate solid material formed in fluid flow communication with the recess. Alternatively, one or more recesses have at least one portion filled with a fluid permeable diffusing medium, thereby to enable dispersed ingress of working fluid into the working chamber.
In accordance with a further embodiment of the present invention, apparatus for inducing controlled perturbations in the flow of the working fluid in one or more working chambers, includes one or more mechanical elastic oscillation generators mounted in association with the inward facing surface or the end walls of one or more working chambers. Thereby, controlled perturbations are caused in the flow of the working fluid in the one or more working chambers. Further apparatus for inducing controlled perturbations in the flow of the working fluid in one or more working chambers, includes one or more generally wear resistant mechanical element freely disposed within the working chamber. The mechanical elements are caused to move within the working chamber by the vortex flow.
In accordance with further embodiments of the present invention and variations thereof, the one or more working chambers include a plurality of working chambers arranged to operate in a predetermined sequence. Each of the plurality of working chambers includes one or more discharge ports for discharging particulate solid material therefrom. Each discharge port has associated therewith apparatus for receiving discharged material therefrom, and for introducing the discharged material into the feed inlet of a predetermined succeeding working chamber of the plurality of working chambers. Also, one or more of the plurality of working chambers includes one or more auxiliary discharge ports formed in the cylindrical side-wall or in the end walls for discharging therefrom a preselected proportion of the discharged particulate solid material. Each of the one or more discharge ports has associated therewith apparatus for receiving the preselected proportion of the discharged material therefrom, and for introducing the preselected proportion of the discharged material into the feed inlet of a predetermined succeeding working chamber.
Additionally, in accordance with further embodiments of the present invention, the end surfaces of the end walls include having one or more rib-shaped baffle fixably attached thereto. Each rib-shaped baffle is concentric with the cylindrical side-wall and serves to reduce the velocity of solid particles adjacent to the end surface to prevent premature discharge of the solid particles. A plurality of concentric cylindrical rib-shaped baffles defines a plurality of concentric annular channels for reducing the velocity of solid particles adjacent to the end surface and thereby prevents premature discharge of the solid particles. The concentric annular channels may also include a plurality of auxiliary fluid inlets for introducing a flow of working fluid within each of the annular channels. These auxiliary fluid inlets are generally in the direction of rotation of the vortex flow. Thus the flow of solid material adjacent to the inner surface of the end wall is accelerated and this results in regulation of the degree of milling of the solid material.
In accordance with an alternative variation of the present invention, rib-shaped baffles are formed as a configuration selected from the group: cylindrical, conical frustum and inverted conical frustum. Further, rib-shaped baffles have predetermined openings formed therein. Alternatively, rib-shaped baffles have predetermined openings formed therein, and vanes disposed adjacent to the openings and external to the circumference of the rib-shaped baffles, thereby to deflect solid particles within the vortex flow away from the inward facing surface of the side-wall and generally towards the vortex axis. The rib-shaped baffles also have predetermined openings formed therein, and have formed thereon vanes disposed adjacent to the openings and internal to the circumference of the ribs, thereby to deflect solid particles within the vortex flow generally away from the vortex axis and towards the inward facing surface of the side-wall.
There is also provided in accordance with an alternative preferred embodiment of the present invention an improved vortex mill for milling a substantially particulate solid material. The mill includes one or more working chambers having a side-wall defining a generally cylindrical, inward facing surface and a first and a second end wall arranged transversely to the side-wall. The end surfaces are formed contiguously with and transversely to the inward-facing surface, thereby to define therewith each of one or more working chambers.
The mill also includes one or more working fluid inlets for introducing a generally tangential flow of working fluid into the one or more working chamber thereby to create a vortex flow therein. One or more discharge ports are formed in one or more of the end walls, for permitting discharge of working fluid and milled material from the one or more working chambers. One or more working fluid inlets together with one or more discharge ports facilitate the vortex flow within the one or more working chambers For introducing a substantially particulate solid material into the one or more working chambers so as to be taken up in a vortex flow of the working fluid, there are one or more feed inlets, thereby to provide milling of the solid material which is discharged from one or more discharge ports. Additionally, there are one or more mechanical insert elements disposed in the inward facing surface of the side-wall or in the end surfaces of the end walls, thereby to induce controlled perturbations in the flow of the working fluid in the one or more working chamber.
In addition, according to another embodiment of the present invention, there is apparatus for inducing controlled perturbations in the flow of the working fluid in the one or more working chambers, thereby to improve the milling of the solid material in the vortex flow.
There is additionally provided, in accordance with a preferred embodiment of the present invention, a process for milling a substantially particulate solid material using an improved vortex mill. The process includes:
introducing a generally tangential flow of working fluid into a generally cylindrical working chamber thereby to create a vortex flow therein;
feeding substantially particulate solid material sought to be milled into the working chamber such that the material is taken up in suspension in the vortex flow, thereby to apply comminution stresses to the suspended solid particles;
inducing controlled perturbations in the vortex flow, thereby to regulate the comminution stresses applied to the suspended solid particles and thus also the rate of milling thereof; and
discharging milled particulate solid material together with working fluid from the working chamber.
There is further provided, in accordance with a preferred embodiment of the present invention, a process in which the step of inducing controlled perturbations includes the step of controlling the extent and frequency of the controlled perturbations of the flow of the working fluid, thereby the rate of milling of the substantially particulate solid material is controlled within the working chamber.
In accordance with other embodiments of the present invention, the process includes the additional step of introducing into the working chamber a flow of working fluid via an inlet disposed at a predetermined angle to the direction of flow of the vortex. Furthermore, the step of controlling the extent and frequency of the controlled perturbations in the flow of working fluid includes adjusting the flow rate of working fluid entering generally tangentially into the chamber. Other steps include altering the feed rate of the particulate solid material, adjusting the flow rate of the working fluid entering non-tangentially into the working chamber, at a predetermined angle to the direction of flow of the vortex; or varying the working fluid pressure in the working chamber. Also, the step of feeding substantially particulate solid material includes the step of pneumatically transporting the substantially particulate solid material into the working chamber.
Further, in accordance with variations of embodiments of the present invention, the vortex flow extending transversely through the working chamber, gives rise to an area of low pressure in the region of the axis. The process step of pneumatically transporting the substantially particulate solid material into the working chamber includes the step of exposing a feed of the material to the low pressure area in the axial region of the vortex, thereby causing material to be drawn into the chamber. Also, the step of pneumatically transporting the substantially particulate solid material into the working chamber includes the step of drawing the substantially particulate solid material into the working chamber via an auxiliary feed inlet. This step utilizes a suction effect caused by the vortex flow tangential to the auxiliary feed inlet. Furthermore, pneumatically transporting the substantially particulate solid material into the working chamber includes operating an ejector with a flow of working fluid thereby drawing the substantially particulate solid material from a feed vessel, and introducing the substantially particulate solid material and working fluid into the working chamber.
In accordance with other embodiments of the present invention, the process step of discharging particulate solid material includes the step of selectively discharging unmilled and oversized particulate solid material thereby controlling the extent of comminution in the working chamber. Also included is a step of introducing the discharged unmilled and oversized particulate solid material into the working chamber for further milling. In addition, the process step of discharging particulate solid material includes the step of discharging particulate solid material from one of a plurality of working chambers. There is also included an additional step of feeding the discharged particulate solid material into a preselected working chamber of the plurality of working chambers for milling therein.